When and how to amend tax return after recharacterizing excess contribution to Roth IRA

Here's my situation:

 

  • In 2018, I contributed the full $5500 to my Roth IRA and filed my 2018 tax returns on time (before April 15, 2018)
  • A week ago, I realized that I was over the income limit for Roth IRA contributions. So after a little research, I learned that I have until Oct 15, 2019 to remove the excess contributions to avoid the 6% penalty. 
  • I recharacterized the excess (plus earnings) to a Traditional IRA.
  • I believe I now need to file an amended 2018 tax return. Not sure exactly what I need to do and by when.
  • FYI, I'm told the 1099-R for this recharacterization is not going to be produced until next year (2020) and I'm not sure if I need to fill out/amend other forms (e.g. 8606, 1040, etc.). I also have an employer sponsored 401K and over the income limit so this will be a non-deductible TIRA contribution.

 

Any help is greatly appreciated!